Why my situationship after the breakup hurt more than i expected

they say that the situationship right after your breakup of long term relationship hits harder, and I believed it, and i tried to avoid it, i was guarding myself. but still, i let myself open to you, i felt at peace, initially it was just a flirt, a rebound of sorts. but with each conversation my attachement to you got deeper. your humour, your mindset, what you have been through, your intelligence resonated with me. for me it was a suprise, to feel connection to someone as quick as it was with you. you were also after breakup, but just recently you revealed what has been on your mind. you still love her, and i understand, i cannot force anything. you saw us as something casual. you were also looking elsewhere, in search for someone new. i did not know that. just yesterday, you revealed this to me. it hurts. we talked about our feelings, i don't love you but i wanted to try with you, i was enchanted by you. but you never saw me this way. i was good to spend night with, to laugh with, to do coupely things with, to share deep thoughts, you special places in your city, to talk for hours on the phone. there was chemistry, but that is not the base for the relationship after all. i was good for all those things but not good enough to consider as something more, a "maybe". and i know that i cannot force it. and to protect myself and you, i needed to put stop to it. we agreed not to talk to eachother, now for a couple of days but i think it will be forever. i don't have what you are looking for, i listened, i encouraged, i was by your side - and i am not angry that i did it, your are amazing, fantastic human being and i am glad that i met you, but there won't be continuation to this story. you have told you therapist to check on you, if they will see any signs of hurting me or yourself, they should stop it. so after all, i can assume that to some point, on a friendship level you cared.
and it was me who stopped it. who asked for clarity. if there is any hope. and there is none. so first, i said that we need clear boundaries, just for friendship. then, couple days later you revealed, that you were thinking about others, of trying with others. and i decided, that we need to stop it, that for now i cannot continue, because the jealousy will destroy me, and i cannot loose any more of myself and any more time.

i know i was confusing, i did not want to admit my feelings. but you were also hiding yours. and it hurts me right now, but i know that being your friend and seeing you happy with somebody else, although i want you to be happy, could possibly affect me to the extend that would be destructive.

the good relationship is build on trust and sincerity, you have told me, and i agree. i have tried, and i confessed, later than i should maybe, but you wouldn't do that.

and as my sign of respect for you, as a sign for my feelings for you and as a sign of me now putting myself first and not dissapearing into other - i have decided to cut it.

please, be happy. i know that you have good people around you that will help you. i know and i saw that you made a huge progress in clearing your mind. i cannot bring another burden to you, and i do not want to introduce more instability to your life. please, keep being amazing as you are, you will acheve everything you are dreaming of. hopefully, one day you will meet that someone special. and hopefully, i will too.

goodbye.